Flexible disks, known as floppy disks, are generally made of plastic and are utilized for recording and reading-out information usually in an off-line mode in a data processing system. These flexible disks are light weight, relatively low cost and convenient to use. The disks are packaged in envelopes formed from sheets of flexible plastic, such as polyvinyl chloride. The envelopes have aligned center or drive holes which allow the enclosed flexible disk to be rotated within the envelope. The envelope is lined with a layer of a low friction wiper material. The envelope includes slots which permit writing and reading into and from the disk.
The flexible plastic envelopes are formed from precut and prepunched sheets of plastic material which have the center drive holes and access slots prepunched therein. Half of a precut sheet or blank is rectangular and the other half is identical, except that it includes three flaps which extend from its three outer edges. The low friction liner or wiping material is attached to the inner surface of the sheet prior to cutting and punching. The envelope is formed by folding each half of the sheet against the other half, making a centerfold therein. The side flaps are folded around the edges of the opposite half of the sheet and are sealed thereto. A flexible disk is then inserted into the envelope and the third or end flap is then folded to complete assembly of the flexible disk and envelope. The folds must be exactly located and formed in order to meet the specifications for the flexible disk unit. If the folds are of too small a radius, the friction between the disk and the liner will increase the torque required by the flexible disk drive system. Too large a fold radius will result in insufficient friction of wiping material against the disk resulting in an out of specification flexible disk unit. Warpage of the completed flexible disk unit must be kept within tight tolerances to produce an acceptable flexible disk system. Locating the centerfold precisely in the middle of the two registration holes eliminates the dimensional difference. That is, the dimensional tolerance between hole centers, and the individual hole diameter tolerances, will be evenly divided about the middle fold of the finished product.
Accordingly, it is the main feature of the invention to precisely locate and form the centerfold in the flexible plastic prepunched sheet to minimize registration hole, misregistration problems.
It is another feature of the present invention to accurately locate and form the centerfold therein so that product blanks which were manufactured in a "worst-case" tolerance condition can be utilized.
The operation of the centerfold forming apparatus also brings the side flap folding apparatus and the sealing apparatus into operating position within the same station.